This research describes the final phase of an ongoing longitudinal study of social development from childhood through late adolescence. A special concern is the organization, determinants, and sequelae of aggressive patterns in the lives of individual children. The first objective is to sharpen the prediction of major problems of adaptation in girls and boys. The second objective is to clarify how these problems may be avoided or ameliorated in the school setting and the community. One cohort of boys and girls (N = 220) in the general school population has been seen yearly since they entered the 4th grade; a second cohort (N = 475) has been seen annually since they entered the 7th grade. Both cohorts are scheduled to complete the 12th grade during this investigation. The developmental epoch which these subjects are now entering--mid to late adolescence--is one where serious problems of school, social, and criminal behavior are expected to emerge full-blown. These problems include school drop-out, grade retention, abusive acts towards others and self-destructive acts toward the self. The research will provide a picture of normal changes in males and females in the organization and expression of assertive/aggressive behaviors from late childhood to late adolescence. It also addresses the problem of how behavior patterns are deflected, in some children, toward violent and assaultive acts. The assessments are multimethod, including measures of the subject's self attributions, the peer social network, evaluations by peers and teachers, maturational status, direct observations of behavior, and school and court records. An idiographic analysis will be made of a subsample of highly aggressive males and females, along with their individually- matched controls. One goal is to identify the factors which buffer vulnerable children from serious problems of adolescence and which facilitate adaptation to school and the community. The core longitudinal study will be supplemented by short-term experiments and a satellite investigation of a state-wide sample of violent and assaultive youth.